In order to monitor information inside a tire, such as an air pressure and a temperature, there has been heretofore performed attachment of a sensor unit to a well portion of a rim, detection of the information inside the tire by use of the sensor unit, and transmission of the result to a receiver outside of the tire by utilizing radio waves (for example, see Japanese patent application Kohyo publication No. Hei 10(1998)-504783).
However, if the sensor unit is attached to the well portion of the rim, a bead toe portion of the tire comes into contact with the sensor unit during attachment and removal of the tire to and from the wheel, particularly, when the tire is removed from the rim. Accordingly, a case for receiving the electronic component is often destroyed.